U.S. patent number 4,935,326 [Application Number 07/136,792] was granted by the patent office on 1990-06-19 for electrophotographic carrier particles coated with polymer mixture.
This patent grant is currently assigned to Xerox Corporation. Invention is credited to John A. Creatura, George R. Hsu.
United States Patent |
4,935,326 |
Creatura , et al. |
June 19, 1990 |
Electrophotographic carrier particles coated with polymer
mixture
Abstract
Disclosed is a carrier and developer composition, and a process
for the preparation of carrier particles with substantially stable
conductivity parameters which comprises (1) providing carrier cores
and a polymer mixture; (2) dry mixing the cores and the polymer
mixture; (3) heating the carrier core particles and polymer
mixture, whereby the polymer mixture melts and fuses to the carrier
core particles; and (4) thereafter cooling the resulting coated
carrier particles.
Inventors: |
Creatura; John A. (Ontario,
NY), Hsu; George R. (Rochester, NY) |
Assignee: |
Xerox Corporation (Stamford,
CT)
|
Family
ID: |
26834640 |
Appl.
No.: |
07/136,792 |
Filed: |
December 22, 1987 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
793042 |
Oct 30, 1985 |
|
|
|
|
Current U.S.
Class: |
430/111.32;
428/407; 430/111.34; 523/206; 524/908 |
Current CPC
Class: |
G03G
9/1131 (20130101); G03G 9/1133 (20130101); G03G
9/1134 (20130101); Y10S 524/908 (20130101); Y10T
428/2998 (20150115) |
Current International
Class: |
G03G
9/113 (20060101); G03G 009/10 () |
Field of
Search: |
;430/108 ;523/206
;524/908 ;428/407 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Welsh; J. David
Parent Case Text
This is a continuation, of application Ser. No. 793,042, filed
October 30, 1985 now pending, the disclosure of which is totally
incorporated herein by reference.
Claims
What is claimed is:
1. A particulate carrier composition for electrophotographic tones
comprised of core particles with a coating thereover comprised of a
fused film of a mixture of first and second polymers which are not
in close proximity in the triboelectric series, said mixture being
selected from the group consisting of polyvinylidene fluoride and
polyethylene; polymethylmethacrylate and copolyethylene vinyl
acetate; copolyvinylidenefluoride tetrafluoroethylene and
polyethylenes; copolyvinylidenefluoride tetrafluoroethylene and
copolyethylene vinyl acetate; and polymethylmethacrylate and
polyvinylidene fluoride.
2. A carrier composition in accordance with claim 1 wherein the
first polymer is present in an amount of from about 10 percent by
weight to about 90 percent by weight, and the second polymer is
present in an amount of from about 90 percent by weight to about 10
percent by weight.
3. A carrier composition in accordance with claim 1 wherein the
first polymer is present in an amount of from about 40 to about 60
percent by weight and the second polymer is present in an amount of
from about 60 to about 40 percent by weight.
4. A carrier composition in accordance with claim 1 wherein the
core is selected from the group consisting of iron, ferrites, steel
and nickel.
5. A carrier composition in accordance with claim 1 wherein the
average particle diameter thereof is from about 30 microns to about
200 microns.
Description
BACKGROUND OF THE INVENTION
This invention is generally directed to developer compositions, and
more specifically, the present invention relates to developer
compositions with coated carrier particles prepared by a dry powder
process. In one embodiment of the present invention the carrier
particles are comprised of a core with coating thereover generated
from a mixture of polymers that are not in close proximity thereto
in the triboelectric series. Moreover, in another aspect of the
present invention the carrier particles are prepared by a dry
coating process wherein a mixture of certain polymers are applied
to the carrier enabling insulating particles with relatively
constant conductivity parameters; and also wherein the
triboelectric charge on the carrier can vary significantly
depending on the coatings slected. Developer compositions comprised
of the carrier particles prepared by the dry coating process of the
present invention are useful in electrostatographic imaging
systems, especially xerographic imaging processes. Additionally,
developer compositions comprised of substantially insulating
carrier particles prepared in accordance with the process of the
present invention are useful in imaging methods wherein relatively
constant conductivity parameters are desired. Furthermore, in the
aforementioned imaging processes the triboelectric charge on the
carrier particles can be preselected depending on the polymer
composition applied to the carrier core.
The electrostatographic process, and particularly the xerographic
process, is well known. This process involves the formation of an
electrostatic latent image on a photoreceptor, followed by
development, and subsequent transfer of the image to a suitable
substrate. Numerous different types of xerographic imaging
processes are known wherein, for example, insulative developer
particles or conductive toner compositions are selected depending
on the development systems used. Moreover, of importance with
respect to the aforementioned developer compositions is the
appropriate triboelectric charging values associated therewith, as
it is these values that enable continued constant developed images
of high quality and excellent resolution.
Additionally, carrier particles for use in the development of
electrostatic latent images are described in many patents
including, for example U.S. Pat. No. 3,590,000. These carrier
particles may consist of various cores, including steel, with a
coating thereover of fluoropolymers; and terpolymers of styrene,
methacrylate, and silane compounds. Recent efforts have focused on
the attainment of coatings for carrier particles, for the purpose
of improving development quality; and also to permit particles that
can be recycled, and that do not adversely effect the imaging
member in any substantial manner. Many of the present commercial
coatings can deteriorate rapidly, especially when selected for a
continuous xerographic process where the entire coating may
separate from the carrier core in the form of chips or flakes; and
fail upon impact, or abrasive contact with machine parts and other
carrier particles. These flakes or chips, which cannot generally be
reclaimed from the developer mixture, have an adverse effect on the
triboelectric charging characteristics of the carrier particles
thereby providing images with lower resolution in comparison to
those compositions wherein the carrier coatings are retained on the
surface of the core substrate. Further, another problem encountered
with some prior art carrier coatings resides in fluctuating
triboelectric charging characteristics, particularly with changes
in relative humidity. The aforementioned modification in
triboelectric charging characteristics provides developed images of
lower quality, and with background deposits.
There is also illustrated in U.S. Pat. No. 4,233,387, the
disclosure of which is totally incorporated herein by reference,
coated carrier components for electrostatographic developer
mixtures comprised of finely divided toner particles clinging to
the surface of the carrier particles. Specifically, there is
disclosed in this patent coated carrier particles obtained by
mixing carrier core particles of an average diameter of from
between about 30 microns to about 1,000 microns, with from about
0.05 percent to about 3.0 percent by weight, based on the weight of
the coated carrier particles, of thermoplastic resin particles. The
resulting mixture is then dry blended until the thermoplastic resin
particles adhere to the carrier core by mechanical impaction,
and/or electrostatic attraction. Thereafter, the mixture is heated
to a temperature of from about 320.degree. F. to about 650.degree.
F. for a period of 20 minutes to about 120 minutes, enabling the
thermoplastic resin particles to melt and fuse on the carrier core.
While the developer and carrier particles prepared in accordance
with the process of this patent, the disclosure of which has been
totally incorporated herein by reference, are suitable for their
intended purposes, the conductivity values of the resulting
particles are not constant in all instances, for example, when a
change in carrier coating weight is accomplished to achieve a
modification of the triboelectric charging charcteristics; and
further with regard to the '387 patent, in many situations carrier
and developer mixtures with only specific triboelectric charging
values can be generated when certain conductivity values or
characteristics are contemplated. With the invention of the present
application, the conductivity of the resulting carrier particles
are substantially constant, and moreover the triboelectric values
can be selected to vary significantly, for example, from less than
-15 microcoulombs per gram to greater than -70 microcoulombs per
gram, depending on the polymer mixture selected for affecting the
coating processs.
With further reference to the prior art, carriers obtained by
applying insulating resinous coatings to porous metallic carrier
cores using solution coating techniques are undesirable from many
viewpoints. For example, the coating material will usually reside
in the pores of the carrier cores, rather than at the surfaces
thereof; and therefore is not available for triboelectric charging
when the coated carrier particles are mixed with finely divided
toner particles. Attempts to resolve this problem by increasing the
carrier coating weights, for example, to as much as 3 percent or
greater to provide an effective triboelectric coating to the
carrier particles necessarily involves handling excessive
quantities of solvents, and further usually these processes result
in low product yields. Also, solution coated carrier particles when
combined and mixed with finely divided toner particles provide in
some instances triboelectric charging values which are too low for
many uses The powder coating process of the present invention
overcomes these disadvantages, and further enables developer
mixtures that are capable of generating high and useful
triboelectric charging values with finely divided toner particles;
and also wherein the carrier particles are of substantially
constant conductivity. Further, when resin coated carrier particles
are prepared by the powder coating process of the present
invention, the majority of the coating materials are fused to the
carrier surface thereby reducing the number of toner impaction
sites on the carrier material. Additionally, there can be achieved
with the process of the present invention, independent of one
another, desirable triboelectric charging characteristics and
conductivity values; that is, for example the triboelectric
charging parameter is not dependent on the carrier coating weight
as is believed to be the situation with the process of U.S. Pat.
No. 4,233,387 wherein an increase in coating weight on the carrier
particles may function to also permit an increase in the
triboelectric charging characteristics. Specifically, therefore,
with the carrier compositions and process of the present invention
there can be formulated developers with selected triboelectric
charging characteristics and/or conductivity values in a number of
different combinations.
Thus, for example, there can be formulated in accordance with the
invention of the present application developers with conductivities
of from about 10.sup.-6 mho (cm).sup.-1 to 10.sup.-17 mho
(cm).sup.-1 as determined in a magnetic brush conducting cell; and
triboelectric charging values of from about a -8 to a -80
microcolulombs per gram on the carrier particles as determined by
the known Faraday cage technique. Thus, the developers of the
present invention can be formulated with constant conductivity
values with different triboelectric charging characteristics by,
for example, maintaining the same coating weight on the carrier
particles and changing the polymer coating ratios. Similarly, there
can be formulated developer compositions wherein constant
triboelectric charging values are achieved and the conductivities
are altered by retaining the polymer ratio coating constant and
modifying the coating weight for the carrier particles.
Other patents of interest include U.S. Pat. No. 3,939,086, which
teaches steel carrier beads with polyethylene coatings, see column
6; U.S. Pat. No. 4,264,697. which discloses dry coating and fusing
processes; U.S. Pat. Nos. 3,533,835; 3,658,500; 3,798,167;
3,918,968; 3,922,382; 4,238,558; 4,310,611; 4,397,935; and
4,434,220.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide toner and
developer compositions which overcome some of the above-noted
disadvantages.
In another object of the present invention there are provided dry
coating processes for generating carrier particles of substantially
constant conductivity parameters.
In yet another object of the present invention there are provided
dry coating processes for generating carrier particles of
substantially constant conductivity parameters, and a wide range of
preselected triboelectric charging values.
In yet a further object of the present invention there are provided
carrier particles comprised of a coating with a mixture of polymers
that are not in close proximity, that is for example, a mixture of
polymers from different positions in the triboelectric series.
In still a further object of the present invention there are
provided carrier particles of insulating characteristics comprised
of a core with a coating thereover generated from a mixture of
polymers.
Further, in an additional object of the present invention there are
provided carrier particles comprised of a core with a coating
thereover generated from a mixture of polymers wherein the
triboelectric charging values are from about -10 microcoulombs to
about -70 microcoulombs per gram at the same coating weight.
In another object of the present invention there are provided
methods for the development of electrostatic latent images wherein
the developer mixture comprises carrier particles with a coating
thereover consisting of a mixture of polymers that are not in close
proximity in the triboelectric series.
Also, in another object of the present invention there are provided
positively charged toner compositions, or negatively charged toner
compositions having incorporated therein carrier particles with a
coating thereover of a mixture of certain polymers.
These and other objects of the present invention are accomplished
by providing developer compositions comprised of toner particles,
and carrier particles prepared by a powder coating process; and
wherein the carrier particles consist of a core with a coating
thereover comprised of a mixture of polymers. More specifically,
the carrier particles selected can be prepared by mixing low
density porous magnetic, or magnetically attractable metal core
carrier particles with from, for example, between about 0.05
percent and about 3 percent by weight, based on the weight of the
coated carrier particles, of a mixture of polymers until adherence
thereof to the carrier core by mechanical impaction or
electrostatic attraction; heating the mixture of carrier core
particles and polymers to a temperature, for example, of between
from about 200.degree. F. to about 550.degree. F., for a period of
from about 10 minutes to about 60 minutes enabling the polymers to
melt and fuse to the carrier core particles; cooling the coated
carrier particles; and thereafter classifying the obtained carrier
particles to a desired particle size.
In a specific embodiment of the present invention there are
provided carrier particles comprised of a core with a coating
thereover comprised of a mixture of a first dry polymer component
and a second dry polymer component. Therefore, the aforementioned
carrier compositions can be comprised of known core materials
including iron with a dry polymer coating mixture thereover.
Subsequently, developer compositions of the present invention can
be generated by admixing the aforementioned carrier particles with
a toner composition comprised of resin particles and pigment
particles.
Various suitable solid core carrier materials can be selected
providing the objectives of the present invention are obtained.
Characteristic core properties of importance include those that
will enable the toner particles to acquire a positive charge or a
negative charge; and carrier cores that will permit desirable flow
properties in the developer reservoir present in the xerographic
imaging apparatus. Also of value with regard to the carrier core
properties are, for example, suitable magnetic characteristics that
will permit magnetic brush formation in mag brush development
processes; and also wherein the carrier cores possess desirable
mechanical aging characteristics. Examples of carrier cores that
can be selected include iron, steel, ferrities, magnetites, nickel,
and mixtures thereof. Preferred carrier cores include ferrites, and
sponge iron, or steel grit with an average particle size diameter
of from between about 30 microns to about 200 microns.
Illustrative examples of polymer coatings selected for for the
carrier particles of the present invention include those that are
not in close proximity in the triboelectric series. Specific
examples of polymer mixtures used are polyvinylidenefluoride with
polyethylene; polymethylmethacrylate and
copolyethylenevinylacetate; copolyvinylidenefluoride
tetrafluoroethylene and polyethylene; polymethylmethacrylate and
copolyethylene vinylacetate; and polymethylmethacrylate and
polyvinylidenefluoride. Other related polymer mixtures not
specifically mentioned herein can be selected providing the
objectives of the present invention are achieved.
With further reference to the polymer coating mixture, by close
proximity as used herein it is meant that the choice of the
polymers selected are dictated by their position in the
triboelectric series, therefore for example, one may select a first
polymer with a significantly lower triboelectric charging value
than the second polymer. For example, the triboelectric charge of a
steel carrier core with a polyvinylidenefluoride coating is about
-75 microcoulombs per gram. However, the same carrier, with the
exception that there is selected a coating of polyethylene, has a
triboelectric charging value of about -17 microcoulombs per
gram.
The percentage of each polymer present in the carrier coating
mixture can vary depending on the specific components selected, the
coating weight and the properties desired. Generally, the coated
polymer mixtures used contains from about 10 to about 90 percent of
the first polymer, and from about 90 to about 10 percent by weight
of the second polymer. Preferably, there are selected mixtures of
polymers with from about 40 to 60 percent by weight of the first
polymer, and from about 60 to 40 percent by weight of a second
polymer. In one embodiment of the present invention, when a high
triboelectric charging value is desired, that is, exceeding -50
microcoulombs per gram, there is selected from about 90 percent by
weight of the first polymer such as polyvinylidenefluoride; and 10
percent by weight of the second polymer such as polyethylene. In
contrast, when a lower triboelectric charging value is required,
less than about -20 microcoulombs per gram, there is selected from
about 10 percent by weight of the first polymer; and 90 percent by
weight of the second polymer.
Also, these results, in accordance with a preferred embodiment of
the present invention, carrier particles of relatively constant
conductivities from between about 10.sup.-15 mho-cm.sup.-1 to from
about 10.sup.-9 mho-cm.sup.-1 at, for example, a 10 volt impact
across a 0.1 inch gap containing carrier beads held in place by a
magnet; and wherein the carrier particles are of a triboelectric
charging value of from -15 microcoulombs per gram to -70
microcoulombs per gram, these parameters being dependent on the
coatings selected, and the percentage of each of the polymers used
as indicated hereinbefore.
Various effective suitable means can be used to apply the polymer
mixture coatings to the surface of the carrier particles. Examples
of typical means for this purpose include combining the carrier
core material, and the mixture of polymers by cascade roll mixing,
or tumbling, milling, shaking, electrostatic powder cloud spraying,
fluidized bed, electrostatic disc processing, and an electrostatic
curtain. Following application of the polymer mixture, heating is
initiated to permit flowout of the coating material over the
surface of the carrier core. The concentration of the coating
material powder particles, as well as the parameters of the heating
step, may be selected to enable the formation of a continuous film
of the coating material on the surface of the carrier core, or
permit only selected areas of the carrier core to be coated. When
selected areas of the metal carrier core remain uncoated or
exposed, the carrier particles will possess electrically conductive
properties when the core material comprises a metal. The
aforementioned conductivities can include various suitable values
Generally, however, this conductivity is from about 10.sup.-9 to
about 10.sup.-17 mho-cm.sup.-1 as measured, for example, across a
0.1 inch magnetic brush at an applied potential of 10 volts; and
wherein the coating coverage encompasses from about 10 percent to
about 100 percent of the carrier core.
Illustrative examples of finely divided toner resins selected for
the developer compositions of the present invention include
polyamides, epoxies, polyurethanes, diolefins, vinyl resins and
polymeric esterification products of a dicarboxylic acid and a diol
comprising a diphenol. Specific vinyl monomers that can be used are
styrene, p-chlorostyrene vinyl naphthalene, unsaturated
mono-olefins such as ethylene, propylene, butylene and isobutylene;
vinyl halides such as vinyl chloride, vinyl bromide, vinyl
fluoride, vinyl acetate, vinyl propionate, vinyl benzoate, and
vinyl butyrate; vinyl esters like the esters of monocarboxylic
acids including methyl acrylate, ethyl acrylate, n-butylacrylate,
isobutyl acrylate, dodecyl acrylate, n-octyl acrylate,
2-chloroethyl acrylate, phenyl acrylate, methylalphachloracrylate,
methyl methacrylate, ethyl methacrylate, and butyl methacrylate;
acrylonitrile, methacrylonitrile, acrylamide, vinyl ethers,
inclusive of vinyl methyl ether, vinyl isobutyl ether, and vinyl
ethyl ether, vinyl ketones inclusive ofvinyl methyl ketone, vinyl
hexyl ketone and methyl isopropenyl ketone; vinylidene halides such
as vinylidene chloride, and vinylidene chlorofluoride; N-vinyl
indole, N-vinyl pyrrolidene; styrene butadiene copolymers; mixtures
thereof; and other similar substances.
As one preferred toner resin there can be selected the
esterification products of a dicarboxylic acid and a diol
comprising a diphenol, reference U.S. Pat. No. 3,590,000 the
disclosure of which is totally incorporated herein by reference.
Other preferred toner resins include styrene/methacrylate
copolymers; styrene/butadiene copolymers; polyester resins obtained
from the reaction of bisphenol A and propylene oxide; and branched
polyester resins resulting from the reaction of
dimethylterephthalate, 1,3-butanediol, 1,2-propanediol and
pentaerthriol.
Generally, from about 1 part to about 5 parts by weight of toner
particles are mixed with from about 10 to about 300 parts by weight
of the carrier particles prepared in accordance with the process of
the present invention.
Numerous well known suitable pigments or dyes can be selected as
the colorant for the toner particles including, for example, carbon
black, nigrosine dye, lamp black, iron oxides, magnetites, and
mixtures thereof. The pigment, which is preferably carbon black,
should be present in a sufficient amount to render the toner
composition highly colored. Thus, the pigment particles are present
in amounts of from about 3 percent by weight to about 20 percent by
weight, based on the total weight of the toner composition,
however, lesser or greater amounts of pigment particles can be
selected providing the objectives of the present invention are
achieved.
When the pigment particles are comprised of magnetites, which are a
mixture of iron oxides (FeO.Fe.sub.2 O.sub.3) including those
commercially available as Mapico Black, they are present in the
toner composition in an amount of from about 10 percent by weight
to about 70 percent by weight, and preferably in an amount of from
about 20 percent by weight to about 50 percent by weight.
The resin particles are present in a sufficient, but effective
amount, thus when 10 percent by weight of pigment, or colorant such
as carbon black is contained therein, about 90 percent by weight of
resin material is selected. Generally, however, providing the
objectives of the present invention are achieved, the toner
composition is comprised of from about 85 percent to about 97
percent by weight of toner resin particles, and from about 3
percent by weight to about 15 percent by weight of pigment
particles such as carbon black.
Also encompassed within the scope of the present invention are
colored toner compositions comprised of toner resin particles,
carrier particles and as pigments or colorants, magenta, cyan
and/or yellow particles, as well as mixtures thereof. More
specifically, illustrative examples of magenta materials that may
be selected as pigments include 1,9-dimethyl-substituted
quinacridone and anthraquinone dye identified in the color index as
Cl 60720, Cl Dispersed Red 15, a diazo dye identified in the color
index as Cl 26050, Cl Solvent Red 19, and the like. Examples of
cyan materials that may be used as pigments include copper
tetra-4(octaecyl sulfonamido) phthalocyanine, X-copper
phthalocyanine pigment listed in the color index as Cl 74160, Cl
Pigment Blue, and Anthrathrene Blue, identified in the color index
as Cl 69810, Special Blue X-2137, and the like; while illustrative
examples of yellow pigments that may be selected are diarylide
yellow 3,3-dichlorobenzidene acetoacetanilides, a monoazo pigment
identified in the color index as Cl 12700, Cl Solvent Yellow 16, a
nitrophenyl amine sulfonamide identified in the color index as
Foron Yellow SE/GLN, Cl Dispersed Yellow 33, 2,5-dimethoxy-4
-sulfonanilide phenylazo-4'-chloro-2,5-dimethoxy acetoacetanilide,
permanent yellow FGL, and the like. These pigments are generally
present in the toner composition an amount of from about 1 weight
percent to about 15 weight percent based on the weight of the toner
resin particles.
For further enhancing the positive charging characteristics of the
developer compositions described herein, and as optional components
there can be incorporated herein charge enhancing additives
inclusive of alkyl pyridinium halides, reference U.S. Pat. No.
4,298,672, the disclosure of which is totally incorporated herein
by reference; organic sulfate or sulfonate compositions, reference
U.S. Pat. No. 4,338,390, the disclosure of which is totally
incorporated herein by reference; distearyl dimethyl ammonium
sulfate; copending application Ser. No. 645,660, entitled Toner
Compositions with Ammonium Sulfate Charge Enhancing Additives, the
disclosure of which is totally incorporated herein by reference;
and other similar known charge enhancing additives. These additives
are usually incorporated into the toner in an amount of from about
0.1 percent by weight to about 20 percent by weight.
The toner composition of the present invention can be prepared by a
number of known methods including melt blending the toner resin
particles, and pigment particles or colorants of the present
invention followed by mechanical attrition. Other methods include
those well known in the art such as spray drying, melt dispersion,
dispersion polymerization and suspension polymerization. In one
dispersion polymerization method, a solvent dispersion of the resin
particles and the pigment particles are spray dried under
controlled conditions to result in the desired product.
Also, the toner and developer compositions of the present invention
may be selected for use in electrostatographic imaging processes
containing therein conventional photoreceptors, including inorganic
and organic photoreceptor imaging members. Examples of imaging
members are selenium, selenium alloys, and selenium or selenium
alloys containing therein additives or dopants such as halogens.
Furthermore, there may be selected organic photoreceptors
illustrative examples of which include layered photoresponsive
devices comprised of transport layers and photogenerating layers,
reference U.S. Pat. No. 4,265,990, the disclosure of which is
totally incorporated herein by reference, and other similar layered
photoresponsive devices. Examples of generating layers are trigonal
selenium, metal phthalocyanines, metal free phthalocyanines and
vanadyl phthalocyanines. As charge transport molecules there can be
selected the aryl diamines disclosed in the '990 patent. Also,
there can be selected as photogenerating pigments, squaraine
compounds, thiapyrillium materials, and the like. These layered
members are conventionally charged negatively thus requiring a
positively charged toner. Other photoresponsive devices useful in
the present invention include polyvinylcarbazole
4-dimethylaminobenzylidene, benzhydrazide;
2-benzylidene-aminocarbazole, 4-dimethaminobenzylidene,
(2-nitro-benzylidene)-p-bromoaniline; 2,4-diphenylquinazoline;
1,2,4-triazine; 1,5-diphenyl-3-methyl pyrazoline 2-(4'
-dimethylaminophenyl)-benzoaxzole; 3-aminocarbazole, polyvinyl
carbazole-trinitrofluorenone charge transfer complex; and mixtures
thereof. Moreover, the developer compositions of the present
invention are particularly useful in electrostatographic imaging
processes and apparatuses wherein there is selected a moving
transporting means and a moving charging means; and wherein there
is selected a deflected flexible layered imaging member, reference
U.S. Pat. Nos. 4,394,429 and 4,368,970, the disclosures of which
are totally incorporated herein by reference.
Images obtained with this developer composition had acceptable
solids, excellent halftones and desirable line resolution, with
acceptable or substantially no background deposits.
With further reference to the process for generating the carrier
particles illustrated herein, there is initially obtained, usually
from commercial sources, the uncoated carrier core and the polymer
powder mixture coating. The individual components for the coating
are available, for example, from Pennwalt, as 301F Kynar, Allied
Chemical, as Polymist B6, and other sources. Generally, these
polymers are blended in various proportions as mentioned
hereinbefore as, for example, in a ratio of 1:1, 0.1 to 0.9; and
0.5 to 0.5. The blending can be accomplished by numerous known
methods including, for example, a twin shell mixing apparatus.
Thereafter, the carrier core polymer blend is incorporated into a
mixing apparatus, about 1 percent by weight of the powder to the
core by weight in a preferred embodiment and mixing is affected for
a sufficient period of time until the polymer blend is uniformly
distributed over the carrier core, and mechanically or
electrostatically attached thereto. Subsequently, the resulting
coated carrier particles are metered into a rotating tube furnace,
which is maintained at a sufficient temperature to cause melting
and fusing of the polymer blend to the carrier core.
Illustrated in FIG. 1 is a graph plotting the negative
triboelectric charge of the carrier in microcoulombs per gram
versus imaging cycles in thousands with a developer composition
comprised of 4 percent by weight of a toner composition containing
styrene butadiene, 78 percent by weight; magnetite commercially
available as Mapico Black, 16 percent by weight; 4 percent by
weight of carbon black; and 2 percent by weight of the charge
enhancing additive distearyl dimethyl ammonium methyl sulfate; and
96 percent by weight of carrier particles consisting of a steel
core with a coating thereover; 0.7 percent by weight of a polymer
blend consisting of 40 percent by weight of polyvinylidenefluoride
and 60 percent by weight of polymethyl methacrylate. The values
reported on this graph were obtained in a Xerox Corporation imaging
test fixture with a photoreceptor imaging member comprised of
aluminum, a photogenerating layer of trigonal selenium dispersed in
polyvinyl carbazole thereover, and a charge transport layer of
N,N'-diphenyl-N,N'-bis(3-methylphenyl)[1,1-biphenyl]4,4'-diamine,
50 percent by weight dispersed in 50 percent by weight of
polycarbonate. This graph thus indicates that the triboelectric
charge, and by inference the carrier coating ratio present remains
relatively constant, that is, about -30 for slightly more than
50,000 imaging cycles, with a 40 to 60 polymer ratio percent weight
respectively.
Illustrated in FIG. 2 is a plot generated in a Faraday Cage, in
accordance with the procedure illustrated hereinafter, of the
negative triboelectric charging values of carrier particles
comprised of a steel core with various polymer ratios thereover of
301F polyvinylidenefluoride, and polyethylene B6 available from
Allied Chemical, which values were at a 1 percent coating
weight.
Also, there can be obtained in accordance with the process of the
present invention carrier particles with positive triboelectric
charging values thereon of from about 10 to about 80 microcoulombs
per gram by, for example, selecting as carrier coatings
polyethylene, and polymethylmethacrylates.
The following examples are being supplied to further define the
present invention, it being noted that these examples are intended
to illustrate and not limit the scope of the present invention.
Parts and percentages are by weight unless otherwise indicated.
EXAMPLE I
There was prepared carrier particles by coating 68040 grams of a
Toniolo atomized steel core, 120 microns in diameter, with 680
grams of a polyvinylidenefluoride, available as Kynar 301F, 1
percent coating weight, by mixing these components for 60 minutes
in a Munson MX-1 Minimixer, rotating at 27.5 RPM. There resulted
uniformly distributed and electrostatically attached, as determined
by visual observation, on the carrier core the
polyvinylidenefluoride. Thereafter, the resulting carrier particles
were metered into a rotating tube furnace at a rate of 105
grams/min. This furnace was maintained at a temperature of
503.degree. F. thereby causing the polymer to melt and fuse to the
core.
A developer composition was then prepared by mixing 97.5 grams of
the above prepared carrier particles with 2.5 grams of a toner
composition comprised of 92 percent by weight of a styrene
n-butylmethacrylate copolymer resin, 58 percent by weight of
styrene, 42 percent by weight of n-butylmethacrylate, and 10
percent by weight of carbon black, and 2 percent by weight of the
charge additive cetyl pyridinium chloride. Thereafter, the
triboelectric charge on the carrier particles was determined by the
known Faraday Cage process, and there was measured on the carrier a
charge of -68.3 microcoulombs per gram. Futher, the conductivity of
the carrier as determined by forming a 0.1 inch long magnetic brush
of the carrier particles, and measuring the conductivity by
imposing a 10 volt potential across the brush, was 10.sup.-15
mho-cm.sup.-1. Therefore, these carrier particles are
insulating.
In all the working examples, the triboelectric charging values and
the conductivity numbers were obtained in accordance with the
aforementioned procedure.
EXAMPLE II
The procedure of Example I was repeated with the exception that
102.0 grams, 0.15 percent coating weight, of polyvinylfluoride was
used. There resulted on the carrier particles a triboelectric
charge thereon of -33.7 microcoulombs per gram. Also, the carrier
particles had a conductivity of 10.sup.-9 mho-cm.sup.-1. Thus,
these particles are considered conductive. Therefore, by changing
the coating weight from 1 percent to 0.15 percent, there is a
significant conductivity change; that is, the carrier particles are
converted from being insulating, reference Example I, to being
conductive, reference the present Example, and the triboelectric
value increased from -68.3 to -33.7.
EXAMPLE III
A developer composition of the present invention was prepared by
repeating the procedure of Example I with the exception that there
was selected as the carrier coating 680 grams of a polymer blend at
a 1.0 percent coating weight of a polymer mixture, ratio 1:9 of
polyvinylidenefluoride, Kynar 301F, and polyethylene, available as
Polymist B6 from Allied Chemical. There resulted on the carrier
particles a triboelectric charge of -17.6 microcoulombs per gram.
Also, the carrier particles were insulating in that they had a
conductivity of 10.sup.-15 mho-cm.sup.-1.
Therefore, there results carrier particles that are insulating and
with a relatively low tribo, namely -17.6 microcoulombs per
gram.
EXAMPLE IV
A developer composition was prepared by repeating the procedure of
Example III with the exception that there was selected as the
carrier coating of a polymer mixture, ratio 9:1, of
polyvinylidenefluoride, Kynar 301F, and polyethylene, available as
Polymist B6. About 680 grams of the polymer blend, that is a 1.0
percent coating weight, was selected. There resulted on the carrier
particles a triboelectric charge of -63 microcoulombs per gram, and
the insulating carrier particles had a conductivity of 10.sup.-15
mho-cm.sup.-1.
Therefore, for example, in comparison to the developer of Example
III with a polymer blend ratio of 9 to 1, instead of 1 to 9, there
was obtained isulating carrier particles with a higher negative
triboelectric charge, namely -63 microcoulombs per gram as compared
to -17.6 microcoulombs per gram with reference to the developer of
Example III.
EXAMPLE V
A developer composition was prepared by repeating the procedure of
Example III with the exception that there was selected as the
carrier coating a blend, ratio 3:2, of a polymer mixture of
polyvinylidenefluoride, Kynar 301F, and high density, 0.962
grams/milliliters, of polyethylene FA520, available from USl
Chemical Company. About 340 grams of the polymer blend, that is a
0.5 percent coating weight, was added. There resulted on the
carrier particles a triboelectric charge of -29.8 microcoulombs per
gram. Also, the resulting insulting carrier particles had a
conductivity of 10.sup.-14 mho-cm.sup.-1.
EXAMPLE VI
A developer composition was prepared by repeating the procedure of
Example III with the exception that there was selected as the
carrier coating a blend, ratio 7:3, of a polymer mixture of
copolyvinylidenefluoride tetrafluoroethylene, available from
Pennwalt as Kynar 7201, and a high density, 0.962 grams per
milliliter, of polyethylene available as Microthene FA520 from USl
Chemicals Company. About 272 grams of the polymer blend, that is a
0.4 percent coating weight, was added. There resulted on the
carrier particles a triboelectric charge of -47.6 microcoulombs per
gram. Also, the resulting insulating carrier particles had a
conductivity of 10.sup.-14 mho-cm.sup.-1.
EXAMPLE VII
A developer composition was prepared by repeating the procedure of
Example VI with the exception that there was selected as the
carrier coating a blend, ratio 7:3, a polymer mixture of
copolyvinylidenefluoride tetrafluoroethylene, available from
Pennwalt as Kynar 7201, and a low density, 0.924 grams per
milliliter, polyethylene available from USl Chemicals Company as
FN510. About 476 grams of the polymer blend, that is a 0.7 percent
coating weight, was added. There resulted on the carrier particles
a triboelectric charge of -42 microcoulombs per gram. Also, the
resulting insulating carrier particles had a conductivity of
10.sup.-15 mho-cm.sup.-1.
EXAMPLE VIII
A developer composition was prepared by repeating the procedure of
Example IV with the exception that there was selected as the
carrier coating a blend, ratio 7:3, of a polymer mixture of Kynar
7201, and a copolyethylene vinylacetate, available from USl
Chemical Company as FE532. About 476 grams of the polymer blend,
that is a 0.7 percent coating weight, was added. There resulted on
the carrier particles a triboelectric charge of -33.7 microcoulombs
per gram. Also, the resulting insulating carrier particles had a
conductivity of 10.sup.-15 mho-cm.sup.-1.
EXAMPLE IX
A developer composition was prepared by repeating the procedure of
Example VIII with the exception that there was selected as the
carrier coating a blend, ratio of 2:3, of a polymer mixture of a
polyvinylidenefluoride available from Pennwalt as Kynar 301F, and a
polymethacrylate available from Fuji Xerox. About 476 grams of the
polymer blend, that is a 0.7 percent coating weight, was added.
There resulted on the carrier particles a triboelectric charge of
-29.5 microcoulombs per gram. Also, the resulting insulating
carrier particles had a conductivity of 10.sup.-15
mho-cm.sup.-1.
With further reference to the above Examples, the conductivity
values were obtained as indicated herein. Specifically, these
values were generated by the formation of a magnetic brush with the
prepared carrier particles. The brush was present within a one
electrode cell consisting of the magnet as one electrode and a
nonmagnetic steel surface as the opposite electrode. A gap of 0.100
inch was maintained between the two electrodes and a 10 volt bias
was applied in this gap. The resulting current through the brush
was recorded and the conductivity is calculated based on the
measured current and geometry.
More specifically, the conductivity in mho-cm.sup.-1 is the product
of the current, and the thickness of the brush, about 0.254
centimeters divided by the product of the applied voltage and the
effective electrode area.
With insulating developers, there are usually obtained images of
high copy quality with respect to both lines and halftones,
however, solid areas of substantially lower quality. In contrast,
with conductive developers there are achieved enhanced solid areas
with low line resolution and inferior halftones.
With respect to the triboelectric numbers in microcoulombs per
gram, they were determined by placing the developer materials in an
8 oz. glass jar, with 2.75 percent by weight toner compositions
placed on a Red Devil Paint Shaker and agitated for 10 minutes
Subsequently, the jar was removed and samples from the jar were
placed in a known tribo Faraday Cage apparatus. The blow off tribo
of the carrier particles was then measured.
Other modifications of the present invention may occur to those
skilled in the art based upon a reading of the present disclosure
and these modifications are intended to be included within the
scope of the present invention.
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